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Thermal B
The series 60 thermal detectors are resettable and operate by using a matched pair of thermistors to sense heat. One thermistor is exposed to the ambient temperature, the other is sealed. In normal conditions the two thermistors register similar temperatures, but on the development of a fire, the temperature recorded by the exposed thermistor will increase rapidly, resulting in an imbalance of the thermistors and causing the detector to change to the alarm state.
Fixed thermal detectors only change to the alarm state at a preset temperature.
Externally, the thermal detectors are distinguishable from smoke detectors by having wide openings to the surrounding atmosphere to allow good movement of air around the external thermistor.
